This invention relates to a video signal processing apparatus that conducts signal processing such as contrast adjustment and edge compensation on a video signal, a TV receiver using such a video signal processing apparatus, and a video signal processing method.
As a conventional technique concerning the contrast compensation function in TV receivers, a technique of detecting a maximum level and a minimum level of a video luminance signal and an average luminance level and controlling the contrast compensation on the basis of these levels is known as described in, for example, Japanese Patent No. 3,215,400. As a conventional technique concerning the sharpness adjustment function, i.e., the edge compensation function, a technique of conducting edge compensation (emphasis) by extracting high frequency components in a video signal and adding the extracted high frequency components to the original image is known as described in, for example, JP-A-5-56308.
In the conventional technique described in Japanese Patent No. 3,215,400, a characteristic of an image is detected, and the signal gain is controlled so as to improve the contrast according to the dynamic range of a display apparatus. When the signal gain is increased, however, then the image amplitude becomes large and in addition noise components contained in the image are also amplified. On the other hand, the edge compensation in the edge compensation circuit is conducted by extracting the high frequency components in the horizontal and vertical direction from the video signal and amplifying the extracted high frequency components as described above. Since the noise components contained in the image also distribute in relative high frequency bands, not only the image edges but also the noise components are also amplified (emphasized) in some cases.
In other words, when the edge compensation is further conducted in a state in which compensation for increasing the contrast is being conducted, the noise components are amplified doubly. In an apparatus having these two compensation functions, therefore, the noise components becomes larger in a state in which the compensation for increasing the contrast is being conducted, and there is a possibility that the image becomes difficult to see in some images because of the influence of the noise. Heretofore, the problem of the noise emphasis in the case where the contrast compensation (especially the compensation for increasing the contrast) and the edge compensation are conducted simultaneously has not been considered.